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arXiv · 1604.08297

Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with Terahertz Cavity Photons

Qi Zhang·Minhan Lou·Xinwei Li·John L. Reno·Wei Pan·John D. Watson·Michael J. Manfra·Junichiro Kono
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Abstract

Nonperturbative coupling of light with condensed matter in an optical cavity is expected to reveal a host of coherent many-body phenomena and states. In addition, strong coherent light-matter interaction in a solid-state environment is of great interest to emerging quantum-based technologies. However, creating a system that combines a long electronic coherence time, a large dipole moment, and a high cavity quality ($Q$) factor has been a challenging goal. Here, we report collective ultrastrong light-matter coupling in an ultrahigh-mobility two-dimensional electron gas in a high-$Q$ terahertz photonic-crystal cavity in a quantizing magnetic field, demonstrating a cooperativity of $\sim$360. The splitting of cyclotron resonance (CR) into the lower and upper polariton branches exhibited a $\sqrt{n_\mathrm{e}}$-dependence on the electron density ($n_\mathrm{e}$), a hallmark of collective vacuum Rabi splitting. Furthermore, a small but definite blue shift was observed for the polariton frequencies due to the normally negligible $A^2$ term in the light-matter interaction Hamiltonian. Finally, the high-$Q$ cavity suppressed the superradiant decay of coherent CR, which resulted in an unprecedentedly narrow intrinsic CR linewidth of 5.6 GHz at 2 K. These results open up a variety of new possibilities to combine the traditional disciplines of many-body condensed matter physics and cavity-based quantum optics.

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Qi Zhang, Minhan Lou, Xinwei Li, John L. Reno, Wei Pan, John D. Watson, Michael J. Manfra, Junichiro Kono. 2016-04-28. Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with Terahertz Cavity Photons. https://doi.org/10.1038/nphys3850

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